1. Field of the Invention
The present invention relates generally to medical devices and treatment methods. More particularly, the present invention relates to methods and apparatus for treating cardiac arrhythmias with vibrational energy.
Cardiac arrhythmias, including ventricular tachycardias and ventricular fibrillation, are a leading cause of morbidity and death in Western societies. A very successful technique for treating such arrhythmias is generally referred to as “ventricular cardioversion and defibrillation,” where electrical energy is applied across the chest to synchronize cardiac rhythm. The use of external cardioversion and defibrillation equipment, i.e. where electrode paddles are placed externally on the chest and where relatively high electrical energy is applied, has been very effective, but of course requires the availability of both the equipment and an operator capable of using the equipment. More recently, implantable cardioverter defibrillator (ICD) devices have come into use, which are programmed to automatically intervene after the onset of an arrhythmia. ICD's stabilize the cardiac rhythm by delivering cardioversion, defibrillation, and pacing therapies as needed. Such ICD's have been shown to improve survival and have become the standard of therapy in patients at risk.
ICD's, however, do suffer from certain disadvantages. At present, ICD designs require one or more electrical leads to be implanted on or within the heart in order to provide pacing, cardioversion and defibrillation energy. Such lead placement requires skilled personnel and subjects the patient to radiation during the implantation procedure. The implanted leads are subject to failure and may cause cardiac perforation, thrombo-occlusion, and infection. Lead failure due to fracture or insulation break has been reported to occur in a significant fraction of the patient population after several years. In contrast, implanted leads used for bradycardia pacing have better reliability than ICD leads due to reduced electrical energy carrying requirements. It would be desirable to be able to use pacing leads, carrying less energy, to defibrillate patients and improve lead reliability. Present ICD's also require a relatively long time to charge capacitors, typically from 10–15 seconds, potentially delaying treatment after a potentially lethal arrhythmia is detected. Delay in treatment also requires higher energy delivery to be successful. Moreover, many patients who have received ICD's find that the electric shocks are painful, and the unpredictable nature of the ICD firing can cause anxiety and fear.
Atrial fibrillation is another form of cardiac arrhythmia and is characterized by rapid and disorganized electrical activity in both the left and right atria of the heart. Atrial fibrillation causes absence of atrial contraction and often atrial enlargement. Although not directly lethal, atrial fibrillation is associated with thrombus formation in the atrial appendages and has the potential for causing thrombolic stroke. The lack of coordinated atrial contraction can reduce cardiac output which can exacerbate other heart conditions. Patients in atrial fibrillation may experience heart failure, chest pain, fatigue, light headedness, and shortness of breath. The rapid and irregular heartbeat and palpitations associated with atrial fibrillation can be very distressing to patients. Thus, while atrial fibrillation is not directly fatal, it can be very distressing to patients and has a potential for increasing mortality from other conditions.
Atrial fibrillation may be controlled using the same techniques applied to ventricular arrhythmias, including both external defibrillators and ICD devices. The shortcomings of both these approaches discussed above, however, are even more of a concern for patients suffering from atrial fibrillation since patients are conscious and alert. Moreover, atrial fibrillation events often occur more frequently than ventricular arrhythmias, and patients are often unwilling to tolerate the pain associated with either external defibrillation or the use of ICD devices on such a frequent basis.
For these reasons, it would be desirable to provide improved methods and devices for the treatment of cardiac arrhythmias, including both ventricular arrhythmias and atrial arrhythmias. In particular, it would be desirable to provide such methods and systems for reducing the level of electrical energy required in order to achieve defibrillation and thus reduce the associated pain and shock. Particularly, it would be desirable if such methods and systems could be applied to both external defibrillation and the use of ICD devices. At least some of these objectives will be met by the inventions described below.
2. Description of the Background Art
Patents describing the treatment of arrhythmias using mechanical shock therapy include U.S. Pat. Nos. 6,408,205; 6,330,475; 6,110,098; and 5,433,731. See also U.S. Pat. Nos. 6,539,262; 6,439,236; 6,233,484; 5,800,464; 5,871,506; 5,292,338; 5,165,403; and 4,651,716, as well as WO 03/070323 and WO 99/61058. Medical publications discussing the effects of ultrasound energy and/or mechanical action on the heart include:    The Antiarrhythmics Versus Implantable Defibrillators (AVID) Investigators: A comparison of antiarrhythmic drug therapy with implantable defibrillators in patients resuscitated from near fatal ventricular arrhythmias. N Engl J Med 1997; 337: 1576–1583.    Bardy G H, Cappato R., Smith W M, Hood M, Rissmann W J, Gropper C M, Ostroff H. The totally subcutaneous ICD system (The S-ICD). PACE. 2002; 24, 578.    Camm A J, Murgatroyd F D. Nonpharmaceutical treatment of atrial fibrillation. In Atrial Fibrillation. Facts from Yesterday—Ideas for Tomorrow. Futura Publishing Company, Inc., Armonk, N.Y., 1994.    Dalecki D, Keller B B, Raeman C H, Carstensen E L. Effects of pulsed ultrasound on the frog heart: I. Thresholds for changes in cardiac rhythm and aortic pressure. Ultrasound in Med. & Biol. 1993; 19:385–390.    Dalecki D, Keller B B, Carstensen E L, Neel D S, Palladino J L, Noordergraaf A. Thresholds for premature ventricular contractions in frog hearts exposed to lithotripter fields. Ultrasound in Med. & Biol. 1991; 17:341–346.    Dalecki D, Raeman C H, Carstensen E L. Effects of pulsed ultrasound on the frog heart: II. An investigation of heating as a potential mechanism. Ultrasound in Med. & Biol. 1993; 19:391–398.    Ellenbogen K A, Wood M A, Shepard R K, Clemo H F, Vaughn T, Holloman K, Dow M, Leffler J, Abeyratne A, Verness D. Detection and management of an implantable cardioverter defibrillator lead failure. JACC. 2003; 41:73–80.    Feldman A and Bristow M. Comparison of medical therapy, resynchronization and defibrillation therapies in heart failure trial (COMPANION). Presented at ACC 2003 Late Breaking Clinical Trials.    Franz M R. Mechano-electrical feedback in ventricular myocardium. Cardiovascular Research. 1996; 32:15–24.    Gibbons R J, Antman E M, Alpert J S, Gregoratos G, Hiratzka L F, Faxon D P, Jacobs A K, Fuster V, Smith S C Jr. ACC/AHA/NASPE 2002 guideline update for implantation of cardiac pacemakers and antiarrhythmia devices: a report of the American College of Cardiology/American Heart Association Task Force on Practice Guidelines (ACC/AHA/NASPE Committee to Update the 1998 Pacemaker Guidelines). Circulation. 2002; 106:2145–2161.    Hu H, Sachs F. Stretch-activated ion channels in the heart. J Mol. Cell Cardiol. 1997; 29:1511–1523.    Kohl P, Hunter P, Noble D. Stretch-induced changes in heart rate and rhythm: clinical observations, experiments and mathematical models. Progress in Biophysics & Molecular Biology. 1999; 71:91–138.    Kohl P, Nesbitt A D, Cooper P J, Lei M. Sudden cardiac death by Commotio cordis: role of mechano-electrical feedback. Cardiovascular Research. 2001; 50:280–289.    Kohl P and Ravens U. Cardiac mechano-electric feedback: past, present, and prospect, Prog. Biophys. Mol. Biol. 2003; 82:3–11.    Lee K L, Hafley G, Fisher J D, Gold M R, Prystowsky E N, Talajic M, Josephson M E, Packer D L, Buxton A E. Effect of implantable defibrillators of arrhythmic events and mortality in the multicenter unsustained tachycardia trial. Circulation. 2002; 106:233–238.    Moss A J, Zareba W, Hall W J, Klein H, Wilber D J, Cannom D S, Daubert J P, Higgins S L, Brown M W, Andrews M L. Prophylactic implantation of a defibrillator in patients with myocardial infarction and reduced ejection fraction. N Engl J Med. 2002; 346:877–933.    Niehaus M, Pirr J, De Sousa M, Houben R, Korte T, Eick O J. Non-contact cardiac stimulation with focused ultrasound pulses. PACE 2003: 26:1023.    Nolte S, Doring J H, Frey A. Mechanically induced ventricular extrasystoles in the isolated perfused guinea-pig heart. Arzneim.-Forsch/Drug Research. 1987; 37(11): 1025–1029.    Reiter M J. Effects of mechano-electrical feedback: potential arrhythmogenic influence in patients with congestive heart failure. Cardiovascular Research. 1996; 32:44–51.    Smailys A, Dulevicius Z, Muckus K, Dauksa K. Investigation of the possibilities of cardiac defibrillation by ultrasound. Resuscitation. 1981; 9:233–242.    Tacker, W A. Fibrillation causes and criteria for defibrillation. In Defibrillation of the heart. Tacker, W A, ed. Mosby-Year Book, Inc., St. Louis, Mo., 1994.